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You still need to record the timezone somewhere and you might as well just stick to ISO8601/RFC3339 format then.

One approach is to store numeric timestamps in UTC format. Then if you do have data stored in a different timezone you have to include the timezone with it. That is the default mode of operation for many of the standard date formats.

If you get timestamp data from a system outside of your control though you always have to make sure you know what it means. At least half the time it seems like a date without a timezone isn't UTC, but in whatever the originating timezone was but the developers didn't include a timezone offset in the data...Timezones....the bane of my existence.

That approach has limits, when DST raises its ugly head (for example, in a calendar scheduler). It's interesting that some of these systems ask you for timezones like "GMT London" - it appears to the user that they're asking for the three letter timezone, 'GMT' - which the user probably knows - but what they're really asking is the TZDB timezone location - which the user probably doesn't.

No I don't. UTC.

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